audio_dir command

The audio_dir command is used for setting the path of the destination directory of the convert_book command, and is where the resulting mp3 file is stored.

require 'cw'

cw do
   book_name 'book.txt'
   book_dir './books'
   audio_filename 'book.mp3'
   audio_dir './audio'
   wpm 18
   convert_book
end